Climate, air quality, and health benefits of a carbon fee-and-rebate bill in Massachusetts, USA

State and regional climate policies in the United States are becoming more prevalent. Quantifying these policies' health co-benefits provides a local and near-term rationale for actions that also mitigate global climate change and its accompanying harms. Here, we assess the health benefits of a carbon fee-and-rebate policy directed at fuel use in transport, residential and commercial buildings and industry in Massachusetts. We find that the air pollution reductions from this policy would save 340 lives (95% CI: 82-590), 64% of which would occur in Massachusetts, and reduce carbon emissions by 33 million metric tons, with 2017 as an implementation year, through 2040. When monetized, the benefits to health may be larger than the benefits from climate mitigation, but are sensitive to valuation methods, discount rates, and the leakage rate of natural gas, among other factors. These benefits derive largely from lower transportation emissions, including volatile organic compounds from gasoline combustion. Reductions in oil and coal use have relatively large benefits, despite their limited use in Massachusetts. This study finds substantial health benefits of a proposed statewide carbon policy in Massachusetts that carries near-term and direct benefit to residents of the commonwealth and demonstrates the importance of co-benefits modeling.